Thermal radiation weapon



Feh 24, 197% 5, c, MacDQNALD 3,49

THERMAL RADIATION WEAPON Filed 001;. 13, 1965 2 Sheets-Sheet 1 IN VENTOR.

Feh 24, 1979 .c. MacD 3,496,867

THERMAL RADIATION WEAPON Filed Oct. 13, 1965 2 Sheets-Sheet 2HlJJHMHHJHHHJ W 4w, INVENTOR.

3,496,867 THERMAL RADIATION WEAPON Gilmour C. MacDonald, 55 WarwickDrive, Rte. 1 Shalimar, Fla. 32579 Filed Oct. 13, 1965, Ser. No. 495,626Int. Cl. F41b /00; C06d 1/00 U.S. Cl. 1026 7 Claims ABSTRACT OF THEDISCLOSURE Field of the invention Napalm bombs and flame throwersemploying thickened jet fuel or gasoline as the combustible, are in wideuse. While they do specific military jobs, and in many cases do themwell, they also have disadvantages. Napalm bombs are difficult to dropprecisely because of aerodynamic factors, and are expensive because thetanks are expended with each drop. Since the products of combustion aregaseous rather than solid, the flame has poor radiation characteristics,so Napalm does little damage outside the fireball. Flame throwers arealso very effective for special military purposes. However, because theyare effective, and because they are short-range weapons, operators offlame throwing equipment receive a great deal of special attention fromthe enemy riflemen and gunners.

Weapons proposed to date, wherein combustible dusts or gaseous fuels aremixed with atmospheric air and detonated, have, in the main, proposedrelatively small individual explosions. The reason for this is that asthe size is increased, the problems in attaining homogeneous mixing withatmospheric oxygen in the precise proportions required for mosteffective detonation become truly formidable. With some fuels, adifference in 1% in the fuel-air ratio can make a difference of severalhundred percent in the severity of detonation.

In contradistinction, the subject invention provides for continuouscombustion (as distinguished from detonation) of the trailed fuel cloudby providing homogeneous and automatic ignition means within the cloudto provide for ignition when that portion of the cloud has been mixedwith suflicient air to support combustion. This assures that allportions of the fuel cloud will eventually ignite and burn, regardlessof discontinuities in the flame front and inhomogenieties in thefuel-air mixture. This in turn means that all the thermal energy in thefuel is released.

Detonative-type combustion is not desirable in a thermal radiationweapon. The Atomic Energy Commission has reported that thermal inputs of3 cal./cm. if delivered in one second, will produce first degree burnsand ignite some types of cloth, whereas a thermal input of 6 cal/cm. isrequired for the same effect 'when the heating occurs over a thirtysecond period. It thu appears probable that radiation periods of up toten seconds would cause very little loss in effectiveness. Conversely,the same report indicates that thermal pulse times of less than onesecond also result in some loss of effectiveness.

The literature reports many efforts, both here and abroad, to developuseable weapons employing detona- 3,496,867 Patented Feb. 24, 1970 tionof fuel-air mixtures. Some attempted to dispense carbon black or coaldust from an airplane and initiate detonation with a delayedhigh-explosive charge. Others attained only limited success by using ahigh explosive to disseminate and ignite light metal dusts. Still othershave investigated liquefied petroleum gases as dispersant/ fuels fordetonation type weapons. To date, none of these have achieved the statusof a standard weapon.

Past efforts to develop useable detonation-type weapons employingfuel-air mixtures have failed because of the difficulty in attaining, bymilitarily practical means, homogeneous and stoichiometric fuel-airmixtures. Unless the mixture is stoichiometric within rather narrowlimits, detonation (or even burning, for that matter) will not occur. Ifnot homogeneous within equally narrow limits, propagation of thedetonation (or burning) will also not occur. For example, acetylene hasa very wide flammability range of from 2.3% to and yet the InternationalCritical Tables indicate that the most effective explosion is achievedwith 9% to 10% acetylene in air. This is a tolerance of about 1% of thetotal range of the explosive limits. By comparison, the lower flammablelimit for propane is 2.3% and the upper limit is only 7.3%, a totalrange of 5%. As pointed out above, only a small fraction of this 5%range will result in a militarily useful explosion. It is thus seen thatdifficulties in attaining homogeneous mixing of the fuel-air cloud instoichiometric ratios and in useful amounts presents a most difficultproblem.

Objects It is a principal object of this invention to provide a chemicalfireball munition that eliminates the problems of achieving homogeneousemixing of the fuel-air mixture in the precise proportions necessary foreffective detonation thereby avoiding extreme criticality of fuel-airmixture ratios permitting combustion to continue for several secondswithout seriously reducing the thermal damage done to personnel andmaterial.

Further objects of this invention include:

(1) The provision of a high-temperature thermally radiating weapon thatis free from ionizing radiations and radioactive fallout in which theenergy release consists of direct thermal radiations, together withvisible light and infrared radiation.

(2) The provision of a weapon capable of exposing personnel and materialwithin the effective range of coverage to a thermal radiation intensitywhich would produce effects varying from first degree burns and theignition of some. types of cloth to third degree burns and theinstantaneous defoliation of trees.

(3) The provision of such weapons wherein much of the energy is radiatedin the visible spectrum, to produce damage to the visual receptors inthe eye, causing instantaneous temporary blindness (dazzling) orpermanent blidness at distances possibly several times that producingskin burns.

(4) The provision of dispensing systems for such weapons that may bereused indefinitely unless jettisoned for air combat reasons with theelimination of bomblets, canisters, or Napalm tanks and providing majorsavings in costs.

(5) The provision of precise placement of the weapon effect by deliveryat very low altitudes of high-speed horizontal fly-by of a trailed dustcloud which slows down almost instantaneously on release.

6) The provision to improve pilot survival by delivering as manymunitions as possible on the first pass over the target and making itpossible for a pilot to fire his guns and/ or rockets at the target,simultaneously with the use of the new Weapons of the. invention.

(7) The provision of means for producing a fireball with a higherthermal output than an airplane, thus diverting heat-seekinganti-aircraft missiles to the fireball.

Other objects and further scope of applicability of the presentinvention will become apparent from the detailed description givenhereinafter; it should be understood, however, that the detaileddescription and specific examples, while indicating preferredembodiments of the invention, are given by way of illustration only,since various changes and modifications within the spirit and scope ofthe invention will become apparent to those skilled in the art from thisdetailed description.

General description These desirable results are accomplished accordingto the invention by employing airborn dispenser means to continuouslydeliver a suitable fuel at a relatively high rate of flow, employingturbulence to mix the fuel with atmospheric air, and providing ignitionmeans within the fuel-air cloud to insure that each increment of thetrailer fuel cloud ignites and burns as soon as it is mixed with enoughoxygen for combustion.

Since aluminum burns to A1 a solid, develops 7.4 Kcal./ g. and has anadiabatic flame temperature of 4770 K., it is a prime choice as a fuelfor a thermal radiation weapon, in spite of the fact that the emissivityof A1 0 is only 0.3 at 1100 C.

Magnesium presently costs 50% more than aluminum, and produces only 5.9KcaL/ g. It is preferred mainly as an additive because it has a highadiabatic flames temperature, and particles of it are easier to igniteand burn faster than aluminum. It is a valuable additive to improve theignition and combustion of other fuels.

In addition to aluminum and magnesium in various finely divided forms,boron, boron carbide, zinc, and zirconium dusts are suitable fuels forradiation-type weapon contemplated by the invention.

In consideration of the increased combustion time permitted by thisinvention, it is contemplated to mix a substantial percentage ofaluminum or magnesium pellets with the powdered fuel. The heavierpellets will fall when released to lower the thermal center of radiationby producing a fiery rain. This addition of metallic pellets will alsoincrease the overall loading density of the weapon.

Detailed description As mentioned above, the emissivity of A1 0 is only0.3 at 1100 C., so additives which raise the emissivity of the fireballwill likewise improved the thermal radiation output. Commercial gellantscomprises of pyrogenic submicron silicon dioxide having an emissivity of0.85 at 1100 C. are available, e.g., Cab-O-Sil. When these are added topowdered metal fuel, they increase the. fireball emissivity. Inaddition, such materials may gel a hydrocarbon fuel (if used with themetal dust) and minimize dust settling problems in the weapon.

Polytetrafluoroethylene powder is a possible gellant/ oxidizer whenadded in small quantities. Magnesium dusts and Teflon may detonate whenmixed in air, but are reported to be compatible when mixed in a liquidhydrocarbon.

There are a number of reasons why a combustible liquid such as jet fuelor gasoline should be used to supply a portion of the themal energy inthe weapon. For example, aluminum dusts can be compacted to a muchhigher density when slurried in a liquid, and the liquid fills theintertitial spaces that would otherwise not be used. Both of theseelfects improved efficiency by increasing the. thermal energy carried ina given volume. Further, use of a liquefied petroleum gas such aspropane mixed with the aluminum dust provides a propellant-dispersant toeject the metal dust and disperse it in the air. Deagglomeration of thealuminum dust during delivery poses no problem, as the propane will boilvigorously (pressure 115 p.s.i.a. at 60 F.) when the fuel container isopened at delivery, breaking up agglomerates.

Continuous automatic ignition of the trailed fuel cloud as it becomesmixed with air can be accomplished by several means. For example, whiteand yellow phosphorus ignites in air at about 86 F. and is very solublein carbon disulfide. An igniter consisting of phophorus dissolved in CScan be added to the liquid propane and aluminum dust in the fuel tank ofthe weapon, Where it remains until the fuel is released. When released,the fuel cloud, including the carbon disulfide, evaporates, thephosphorus particles mix with air, oxidize, and ignite, touching off theCS vapors, the propane and the aluminum dust.

Because the ignition energy required by carbon disulfide is very low,and because of the ability to dissolve large quantities of phosphorus,CS is an attractive fuel additive for this purpose. Alternately, thelimited solubility of phosphorus in liquid propane may be used forignition purposes without an intermediate such as CS Other pyrophoricsubstances can be used to insure complete ignition of the gas cloud. Forexample, the trialkyl boranes (trimethyl, triethyl, tripropyl andtributyl boranes) have been investigated as possible additives for jetfuel to prevent flameouts. Organo boron compounds known to bespontaneously flammable in air include triethylboron andtetraethyldiborane. Useable pyrophoric trialkylaluminum compoundsinclude trimethylaluminum and triethylaluminum.

During the early dissemination of the fuel cloud, there will be littleatmospheric air mixed with the fuel, and the resultant mixture will bevery rich. Since the upper explosion limit for propane is only 7.3%, itis advantageous to use additives with a wider range of explosive limits,e.g., acetylene. It is inexpensive, has a very high heat content,requires very little energy for ignition, and has flammability limits offrom 2.3% to Further, it is very soluble in acetone, especially at thepressures necessary to liquefy propane. Acetylene as an additive mayalso improve the ignitability of the aluminum dust. Initial combustionof the acetylene would be under fuelrich conditions, forming carbonblack, which would deposite on the metal dust particles. This blackcoating would increase the absorption of thermal radiation and improveignition. Somewhat the same effect can be attained by the addition ofcarbon black or similar substances directly to the aluminum powder.

When compatible with the fuels selected, other possible additives havinga wide range of flammable limits include unsysmmetricaldimethylhydrazine (flammable limits 2 to and diborane which hasflammable limits of 0.9 to 98% and ignites spontaneously in air at roomtemperature. Diborane may serve as an automatic ignition source asdiscussed above. Propyl nitrate has flammable limits from 2 to 100% andits ignition energy is very low, being comparable to hydrogen, acetyleneand carbon disulfide. Ethyl nitrate, and highly explosive methylnitrate, are also in this general category, as are ethylene oxide,nitromethane, and diethyleneglycol dinitrate.

Examples and drawings For a more complete understanding of the natureand scope of this invention, reference may be had to the followingdetailed description thereof taken in connection with the accompayingdrawings, in which:

FIGURE 1 is a side sectional view of a form of this invention which isadapted to external carriage on fighter aircraft. A liquefied petroleumgas such as propane serves as a propellant/dispersant to dispense aprimary fuel of aluminum dust. :In this simplest form of the invention,a pyrophoric substance such as white phosphorous is dissolved in theliquid propane to provide for continuous, automatic, and homogeneousignition of all portions of the dust cloud as soon as the propane hasvaporized and mixed with air on release. It will be recognized that thissimple form of the invention is not without some hazard, in that it isalways under pressure, and that any leak,

however small, will aways catch fire. However, by the same token, therecan be no explosion, as the fuel will burn as fast as it leaks out intothe air.

FIGURE 2 is a similar sectional view, differing only in that the fuel isdelivered by a pump instead of the vapor pressure of propane. Jet fuelor gasoline would be the liquid portion of the fuel. If thisconstruction is struck by a bullet, some of the fuel mixture could runout of the hole (unless the liquid portion of the fuel was gelled asmentioned above), and would burn as above. However, this fuel flow atworst would be only a very small portion of that from the constructionof FIG- URE 1, wherein the internal pressure will be of the order of 100p.s.i. Safety is increased at a cost in efficiency and complexity.

FIGURE 3 is a schematic diagram of an alternate construction adapted forinternal carriage in large cargo aircraft. In addition to providing forpump delivery of the fuel, the pyrophoric igniter solution is mixed withthe primary fuel just before being sprayed into the air. Thus, the firehazard should be about the same as any other aircraft with a largeamount of fuel aboard. Under some circumstances, it might even be safer,because the main fuel tank of the weapon can be emptied in seconds bythe pump if necessary.

As seen in FIGURE 1, a preferred embodiment of the invention comprisesaerodynamically-shaped fuel tank 11, which contains the fuel, a slurryof aluminum dust in liquid propane, together with pyrogenic additives,and is attached to its supporting pylon on the airplane by means ofshackles 12. This fuel mixture boils violently when the outlet valve 14is opened, the said fuel mixture passing through the outlet pipe 13, theoutlet valve 14 and the divergent nozzle 15, where a portion of the flowimpacts the diverter 16. This diverter has a duel function, the firstbeing to produce a maximum of furbulent mixing of the fuel and air, andthe second being to develop enough reverse thrust to exactly cancel therocket-type thrust developed by the fuel flow. This will permit firingunder-wing dispensers individually without causing the aircraft to yaw.

In a second embodiment of this invention as depicted in FIGURE 2, anaerodynamically-shaped fuel tank 21 contains the fuel, a slurry ofaluminum dust in gasoline or jet fuel. The fuel includes additives toproduce selfignition when mixed with air. Actuation of the pump 24 drawsfuel through section pipe 23 and forces it out divergent nozzle 25. Aportion of the How impacts diverter 26, which functions as above.

In the event that safety considerations, such as the amount of heatradiated to the carrier aircraft, make it necessary to drop thedispenser before actually dispensing and igniting the fuel, thediverters 16 and 26, may be designed to produce substantial reversethrust when fired. When released, the dispenser will then slow rapidlywith respect to the carried aircraft while dispensing the fireball.

A third embodiment of this invention, adapted to deliver largequantities of fuel from cargo-type aircraft, is shown in FIGURE 3. Themain fuel tank 31 contains a slurry of aluminum dust in gasoline or jetfuel, and will usually be mounted in the fuselage of a cargo aircraft.To operate the weapon, the main fuel pump 33 is actuated, drawing fuelthrough suction pipe 32, and forcing it through the pump 33, and theinjector body 34. Concurrently, igniter fuel pump 37 sucks a solution ofphosphorous in carbon disulfide from tank 35 through pipe 36 forces itthrough the pump 37 and out through injector nozzle 38 where it is mixedwith the main flow of fuel. This mixed flow passes through outlet pipe39 into distribution manifold 40 which sprays it into the air asindicated by the arrows.

The foregoing specification discloses a new and useful thermal radiationweapon. While specific examples have been given, applicant claims thebenefit of a full range of equivalents within the scope of the appendedclaims.

I claim:

1. An airborne thermal radiation weapon comprising in combination withan aircraft, a fuel container, a homogeneous mixture of a liquidcombustible fuel, a combustible finely-divided metal and an ignitionmaterial, said ignition material being a substance which automaticallyignites on contact with air, means to discharge said mixture from saidcontainer at a high rate of flow and means to produce turbulent mixingof said mixture with air as said mixture discharges from said container.

2. A radiation weapon as claimed in claim 1 wherein said turbulentmixing means comprises a deflector to cause at least a part of saidmixture to flow in a manner to cancel the net thrust resulting from saidmixture discharge.

3. A thermal radiation weapon comprising in combination a fuel containerenclosing combustible fuel material comprising combustible finelydivided metal, combustible organic liquid and an incombustible additiveto improve thermal radiation characteristics of the fuel material, meansto continuously discharge the fuel material from said container, mixingmeans to produce turbulent mixing of said material with. air as saidfuel material is discharged from said container and ignition means toignite the resulting fuel material and air mixture.

4. A weapon as claimed in claim 3 wherein said additive is finelydivided silicon dioxide.

5. A weapon as claimed in claim 3 wherein said fuel material comprisespolytetrafluoroethylene powder as an oxidizer/gellant.

6. A weapon as claimed in claim 3 wherein said turbulent mixing meanscomprises a deflector to cause at least a part of said fuel material toflow in a manner to at least partially cancel the net thrust resultingfrom said fuel material discharge.

7. In a device for producing aerial fireballs, the combinationcomprising an aircraft carrying fuel container means, a combustible fuelmaterial contained in the fuel container means, said fuel materialcomprising finely divided primary fuel selected from the groupconsisting of aluminum, magnesium, boron, boron carbide, zinc, zirconiumand carbonaceous material in a liquid hydrocarbon, fuel discharge meansadapted to vaporize said fuel material and to intimately andcontinuously mix said fuel material with ambient air as the fuelmaterial is discharged from said fuel container means, said fuelmaterial including means to continuously and automatically ignite allportions of the mixture of said fuel material and ambient air.

References Cited UNITED STATES PATENTS 2,372,264 3/1945 Firth 10262,535,309 12/1950 Mari 1O234.4 3,106,238 10/1963 Bruce 891 X 3,150,8489/1964 Lager 102-344 X 3,188,954 6/1965 Roach et al. 1026 SAMUEL W.ENGLE, Primary Examiner US. Cl. X.R. 1029, 66

